The present invention relates to the thermal treatment of metallurgical products, particularly, thin slabs, which are obtained by continuous casting and which subsequently have to be subjected to a rolling operation.
In mills for direct rolling of metallurgical products, such as thin slabs, obtained from one or two continuous-casting machines, it is necessary to subject the products, before they pass through the rolling mill, to a thermal rehomogenization and, if appropriate, heating treatment, in order to give the products uniform physical characteristics which make it possible to adhere to the rolling tolerances and obtain products of very high quality or top grade. Moreover, by ensuring good thermal homogeneity between slabs and a good temperature reproducibility, whatever the casting conditions, it is possible to obtain the rolling tolerances easily by means of simple adjustments of the rolls of the rolling mill.
To solve the problems thus presented, the present proprietor designed a roller furnace equipped with heating elements which are produced in the form of fossil-fuel burners having a high pulse. Moreover, similar results can be obtained by using heating means consisting of radiant elements.
In this type of known installation, the heating and homogenization of the products, such as thin slabs, are obtained by means of a travel of the slabs at a controlled speed through said roller furnace, in order to ensure a suitable dwell time of these slabs in the successive heating and then homogenization zones which compose the roller furnace. Because of the pronounced deviations which can exist between the temperatures of the start, middle and end of casting, to satisfy the heating requirements before homogenization it is necessary to provide installed heating powers corresponding to the most pronounced deviations and to define a dwell time and therefore a length of heating zone corresponding not only to this maximum temperature deviation, but also to the highest casting speeds.
This known solution has a major disadvantage in that, when it is used on a single continuous-casting line with a single rolling mill, it results in a minimum furnace length of the order of 100 to 150 m, depending upon the relative casting and rolling speeds and the product storage needs, and in deviations between installed powers and used powers of 1 to 10, depending on the entry temperature of the slab, thus making it difficult to operate the heating zones.
The development of mills comprising two continuous-casting lines and a single rolling line gives rise to installation lengths which can prove excessive in some configurations because of the necessary transfers of slabs from either one of the casting lines towards the rolling line, on the one hand, and the necessity to reserve a minimum storage zone to deal with transient situations, on the other hand.